Evaluation of Multi-Constellation GNSS Precise Point Positioning (PPP) Techniques in Egypt

Transcription

1 Evaluation of Multi-Constellation GNSS Precise Point Positioning (PPP) Techniques in Egypt Mahmoud Abd Rabbou and Adel El-Shazly Department of Civil Engineering, Cairo University Presented by; Dr. Mahmoud Abd Rabbou

2 Introduction Based on the correlated nature of the GNSS errors and biases, GNSS differential positioning technique is used to eliminate these errors and biases reaching to centimeter level accuracy. However, using a reference station is considered to be problem for some applications since the operational range is limited to about 15 Km. Moreover, the system cost and complexity is increased. On the other hand, an alternative technique, which is commonly known as precise point positioning (PPP), can achieve comparable positioning accuracy, without extra infrastructure.

3 Introduction By careful modeling of all errors and biases, a single GNSS receiver can achieve a centimeter and decimeter level positioning accuracy for static and kinematic applications based on the satellite availability and geometry, quality of observations. Limited satellites availability and poor geometry in urban canyons and downtown areas severely degrade positioning accuracy. Consequently, multi satellites navigation systems such as GPS, GLONASS, Galileo and BieDou observations can be used to overcome this limitation. In Egypt, at the moment, signals of Satellite Navigation Systems (SNS) as GPS and GLONASS, Galileo and BeiDou could be logged; however, since Galileo is still in Initial operation capability (IOC), observations of one to three satellites could be logged.

4 Research Objectives This research aims to: 1. Investigate the performance of the dual-frequency PPP based technique in Egypt in comparison of the current GNSS differntial positioning solution for high accurate Navigation applications 2. Investigate the performance of the single frequency PPP based technique in Egypt and investigate the accuracy of the Global ionospheric maps accuracy and realibilty 3. Investigate the contribution of the additional Galileo and BeiDou systems observations on the traditional GPS/GLONASS PPP positioning accuracy and convergence time.

5 Mathematical Models The positioning accuracy of a Precise Point Positioning is mainly depending on the ability to mitigate errors and biases which affect GNSS observations. These errors and biases include the satellite/receiver clock errors, satellite/receiver hardware delays, ionospheric and tropospheric delays, and multipath. Moreover, using multi-constellations satellite systems, with different references frames, in a PPP model, introduces additional errors such as time offset between systems, due to the fact that each system uses a different time frame.

6 Mathematical Models s s G G r G G G G G G P=ρ +c(dt +d )-cd t -c(b )+T +I +e s s J J r G J J J J J J P=ρ +c(dt +d )-cd t -c(b )+c[ ISB ] +T +I +e s s s s G G r G G G G G G G G G G G Φ =ρ +c(dt +d )-cd t -c(b )+T -I +[ N +c( -d )-c( -d )]+ s s s s J J r G J J J J J J J J J J J Φ =ρ +c(dt +d )-cd t -c(b )+c[isb ]+T -I +[ N +c( -d )-c( -d )]+

7 Mathematical Models For dual frequency PPP model, the ionosphere free linear combination is used 2 2 f1 P1 f2 P2 s s1 s r r1 r2 f1 f2 P = =ρ +cdt -cdt +T+c(Ad -Bd ) c(ad -Bd )+e 2 2 f1 Φ1 -f2 Φ2 s s1 s r r1 r2 f1 -f2 Φ = =ρ +cdt -cdt +T+c(Aδ -Bδ )+c(aδ -Bδ )+( λn )+ε We apply the ionosphere-free linear combination model on the different GNSS constellations namely, GPS, GLONASS, Galileo and BeiDou.

8 Mathematical Models The General Mathematical model can be written as r s s 3G G r G G G G G P =ρ +c[dt +B ]-c[dt +B ] +T +e r s s 3E E r G E E E E E r s s 3R R r G R R R R R P =ρ +c[dt +B ]-c[dt +B ]+T +c[isb ]+e P =ρ +c[dt +B ]-c[dt +B ]+T +c[isb ]+e r s s 3C C r G C C C C C r s s r s 3G G r G G G G G G r s s r s 3E E r G E E E E E E P =ρ +c[dt +B ]-c[dt +B ] +T +c[isb ] +e Φ =ρ +c[dt +B ]-c[dt +B ]+T +( λn+δb +ΔB ) +ε Φ =ρ +c[dt +B ]-c[dt +B ]+T +c[isb ]+(λn+δb -ΔB ) +ε r s s r s Φ 3R=ρ R +c[dt r+b G ]-c[dt R+B R ]+T R+c[ISB R ]+(λn+δb -ΔB ) R+εR r s s r s Φ 3C=ρ C +c[dt r+b G ]-c[dt C+B C ]+T C+c[ISB C ]+(λn+δb -ΔB ) C+εC

9 Analysis and Results Both the single frequency and dual frequency PPP techniques are processed in two data sets collated in Egypt using Trimble R8 receiver for more than 9 hours duration. The data logged to collect the four GNSS constellations namely: GPS, GLONASS, Galileo and BeiDou The relative positioning for the two points are taken as a reference solution The final precise products of the International GNSS Service multi-gnss experiment (IGS-MEGX) network are used to account for the GNSS satellite orbit and clock errors (Montenbruck et al., 2014). For single frequency model, The ionospheric delay is largely corrected through the IGS global ionosphere maps (GIM) model (Schaer et al., 1998). The hydrostatic and wet components of the tropospheric zenith path delay are modelled through the UNB3 model. All remaining errors and biases are accounted for using existing models (Kouba 2009).

10 Analysis and Results (DF-PPP)

11 Analysis and Results (DF-PPP) GNSS-PPP Combinations Latitude (m) Longitude(m) Altitude (m) RMSE Max RMSE Max RMSE Max GPS GPS/GLONASS GPS/BeiDou GPS/Galileo GNSS The positioning accuracy after 15 mins

12 Analysis and Results (SF-PPP)

13 Analysis and Results (SF-PPP) GNSS-PPP Combinations Latitude (m) Longitude(m) Altitude (m) RMSE Max RMSE Max RMSE Max GPS GPS/GLONASS GPS/BeiDou GPS/Galileo GNSS

14 Conclusion This research investigate the performance of multi-constellation GNSS Precise Point Positioning in Egypt. Both single frequency and dual frequency GNSS PPP models are processed. Different GNSS PPP combinations were assessed namely, GPS only,, GPS/GLONASS, GPS/BeiDou, GPS/Galileo and finally multi-constellation GNSS PPP. For dual Frequency PPP. The results indicate that the convergence time for the combined GNSS PPP was enhanced compared with the standard GPS PPP convergence time. The main contribution is attributed to the additional GLONASS observations while marginal enhancement can be detected from Galileo and BeiDou. After15 mins of processing, the GPS PPP achieve decimetre level accuracy while the additional GLONASS observation enhance the positioning solution to centimetre level accuracy.

15 Conclusion For Single Frequency GNSS PPP. The final IGS GIM model was used to account for the ionospheric delay. The contribution of the additional GNSS observations to the PPP solution was assessed through comparison with the traditional GPS-only counterpart. It was shown that the contribution of the additional GLONASS observations is significant, while the contribution of both Galileo and BeiDou can be consider marginal due to their limited satellite availability.